Contagious Ecthyma in Sheep and Goats: Recognising the Lesions and Ruling Out Key Differentials

A lamb with thick crusts around the lips may initially look like a straightforward skin case. But when several animals develop painful oral and facial lesions, the diagnosis needs a closer look. Is the lesion pattern typical of contagious ecthyma, or could another important disease be involved? 

Contagious ecthyma, commonly known as orf or sore mouth, is caused by Orf virus (ORFV), a member of the genus Parapoxvirus in the family Poxviridae. Sheep and goats are most commonly affected, although infection can occur in other ruminants as well^[1]. 

The Lesion Pattern Can Point Towards Orf 

ORFV gains entry through breaks in the skin. Grazing animals may sustain small abrasions from dry, stemmy or prickly feed, particularly around the lips, nostrils and oral tissues. The virus then multiplies in epidermal cells and produces the characteristic proliferative skin lesions. 

The clinical progression typically moves through erythema, papules, vesicles, or pustules and crust formation. Lesions are most often seen on the lips, snouts, nostrils, eyelids, ears, and tongue. However, the disease can extend beyond the face, with lesions reported on the legs, feet, and udders. 

The lesions can become thick, sticky and painful. This is particularly important in young animals. When lesions interfere with nursing or grazing, affected lambs and kids may eat less or stop feeding altogether. Severe cases can therefore progress to anorexia and starvation^[2]. 

Lesions generally resolve gradually, although the clinical course can extend for several weeks. Peralta et al. described progression from redness and blisters to bumps and crusts, followed by gradual improvement over one to two months^[1]. 

When Should Another Disease Be Considered?^[1] 

A crusted lesion around the mouth should not automatically be labelled as orf. 

Foot-and-mouth disease (FMD) is an important differential when oral lesions are present. In sheep, FMD lesions are particularly likely to involve the lower gums and tongue. Orf, in contrast, is characterised by proliferative lesions, providing an important clinical distinction. 

Ulcerative dermatosis can also produce facial, foot, and genital lesions accompanied by inflammation and crust formation. Sheep and goat pox should be considered when elevated papules are distributed more widely over the body, and the clinical picture is more severe. 

The distribution of lesions therefore matters. Facial and oral proliferative lesions that progress into characteristic crusts support orf, while an unusual distribution or lesion pattern should prompt reconsideration of the differential diagnosis. 

Confirming the Diagnosis When the Picture Is Unclear 

Clinical examination can be sufficient when the lesions and disease progression are characteristic. However, laboratory confirmation becomes valuable when clinical findings overlap with other diseases. 

PCR is particularly useful for detecting ORFV. The B2L (ORFV011) and F1L (ORFV059) genes are commonly targeted for ORFV diagnosis. Real-time PCR can also detect viral DNA and may be useful when rapid confirmation is needed during an outbreak. 

Electron microscopy can help identify parapoxvirus based on its characteristic ovoid virion and crisscross surface tubules. However, it cannot distinguish the virus to species level^[3]. 

Serological methods, including ELISA, have also been used for parapoxvirus detection. Virus neutralisation testing is less commonly used for ORFV diagnosis because cell-mediated immunity plays an important role in protection, and neutralising antibody concentrations may be low^[4]. 

Clinical Bottom Line 

For practicing veterinarians, lesion location, morphology, and progression should be assessed together. Proliferative lesions around the lips, muzzle, and oral region strongly support contagious ecthyma. 

FMD, ulcerative dermatosis, and sheep/goat pox should remain key differentials when lesions are atypical or widely distributed. FMD commonly affects the lower gums and tongue; ulcerative dermatosis may involve the face, feet, and genitalia, while sheep/goat pox can produce elevated papules across the body. When clinical findings are uncertain, PCR can confirm ORFV involvement.

References:

1. Bhagawati N, Shankarishan P, Habibi M. Contagious ecthyma in goat and sheep: a review of current status and future perspectives. https://mbimph.com/index.php/UPJOZ/article/view/4982/6394
2. Chan KW, Lin JW, Lee SH, Liao CJ, Tsai MC, Hsu WL, Wong ML, Shih HC. Identification and phylogenetic analysis of orf virus from goats in Taiwan. Virus genes. 2007 Dec;35(3):705-12. https://www.researchgate.net/profile/Wei-Li-Hsu-3/publication/6156481
3. Hosamani M, Scagliarini A, Bhanuprakash V, McInnes CJ, Singh RK. Orf: an update on current research and future perspectives. Expert review of anti-infective therapy. 2009 Sep 1;7(7):879-93. https://www.academia.edu/download/41885833/Orf_An_update_on_current_research_and_fu20160202-30232-6wkxr.pdf
4. Krešić N, Šimić I, Bedeković T, Acinger-Rogić Ž, Lojkić I. Evaluation of serological tests for detection of antibodies against lumpy skin disease virus. Journal of clinical microbiology. 2020 Aug 24;58(9):10-128. https://journals.asm.org/doi/pdf/10.1128/jcm.00348-20